How-To: calculate your HP from your track slip

[sonyman87]

here is how ya do it.

 

take your vehicle weight / (ET/5.825)^3

 

so for me with my ET at 15.070 my HP at the wheels is

if my car is 3400lbs

 

3400/(15.07/5.825)^3 = 196.348 HP

 

if my car weighs

3600lbs <-- most likely closer to this figure.

 

then

 

3600/(15.07/5.825)^3 = 207.89HP!

 

to figure HP at the flywheel. simply take that wheel HP number by drive train loss. with a 1 infront of it. say the 4t60e is at a 22% loss then i would take wheel HP * 1.22

 

this gives me ruffly 239.54-253.64 HP at the crank.

 

thats only 30-40hp over stock. waaa hoo for bolt-ons.

[john99gtp]

According to those calcs

 

 

274.4548146300118027510067344675 HP

 

 

is this WHP or crank HP??

 

If this is crank, i say thats right on. If its wheel, i say its way off.

[Cam'ron]

:oops: what the hell is the ^3 thing i am a math idiot!

[maybe2fast]

to the power of 3

[Cam'ron]

:oops:

[sonyman87]

According to those calcs

 

 

274.4548146300118027510067344675 HP

 

 

is this WHP or crank HP??

 

If this is crank, i say thats right on. If its wheel, i say its way off.

 

where you getting 274 from???

~3600lbs = car + you + fuel etc..

(14.0/5.825) ^3 = 14.88xxx 3600/14.88 = 259.xx

with your 14.0 run you got 259 wheel HP and i dont know the powertrain loss on the 5t65e.. thats probably around 17% so that equates to around 300 crank HP. which would be about dead on for a 14 second car.

[mfewtrail]

Are you counting the weight of the car with you in it? I'll guess 3400lbs for my TGP with me in it.....so 211whp going by that(14.705 ET ). I want to dyno the car soon and get some real numbers, as well as going to the track again when it gets cool/cold here to try to run some better times.

[sonyman87]

Are you counting the weight of the car with you in it? I'll guess 3400lbs for my TGP with me in it.....so 211whp going by that(14.705 ET ). I want to dyno the car soon and get some real numbers, as well as going to the track again when it gets cool/cold here to try to run some better times.

 

weight of the car is figured in the equation..

 

at 3400 pounds 211whp would be correct if thats what the car weighed at the time of the run. obiously the more accurat the weight of the car the more closer you will be to an acutal number

 

257 crank hp is what i get after your 4t60 auto trans 22% loss.

[sl3196]

Just go to a dyno....

[mfewtrail]

211whp assuming 22% loss would be 270hp at the crank.

 

 

To calculate crank hp from whp when assuming a certain loss percentage do the following.

 

Example(using the 211whp & 22% loss): Add two zeros to the whp figure and then divide by 100 subtract the percentage number(100 subtract 22 in this case)...so you end up with 21100/78 = 270.5 hp Basically you're just setting up a proportion of sorts with one unknown and solving it.....I just don't write down the figures as a proportion.

[john99gtp]

3830/(14.024/5.825)^3

 

Rounding to third decimal place:

 

so you do 14.024/5.825 = 2.408

 

2.408^3 = 13.955

 

3830/13.955 = 274.455HP

 

I say if its WHP its off (cause i pulled 231WHP) but if its crank, its closer, since (according to the equation below) 231/.82 = 281HP at the crank.

 

 

Did you perhaps write the equation wrong?? From what you wrote, im going by OOO (order of operations) so parenthesis, then powers, then divide everything by what you got for the bottom.

[joey b]

the 4T60e has a 18% drivetrain loss. The 5 speed 15%. I'd bet that the 65 is somewhere just a tad higher than the 60, so 18.5-19%. A bunch of guys from efi ran at a dyno a couple of years ago and I remember that is what the guy at the dyno estimated. BTW, if you have 100 WHP and 18% loss you would take 100/.82 to get an accurate crank HP.

[streetdreams]

I've heard of an equasion like that before but it cant be that accurate can it? I mean I could run the same car on bald tires and than again on slicks and get 2 different readings? I think theres alot of things which could effect your timeslip thus effect your hp equasion

[sonyman87]

I've heard of an equasion like that before but it cant be that accurate can it? I mean I could run the same car on bald tires and than again on slicks and get 2 different readings? I think theres alot of things which could effect your timeslip thus effect your hp equasion

 

well it only gives you the actual amount of power the car exerts at the time of the run. a dyno uses the same type of formula. except it uses the drums to calculate the power instead of the car itself.

 

+

i dont think i believe a 3850lb prix.. thats way to heavy.. i think the scale he used was a tad bit off.

[john99gtp]

well, i weighed it once, it was 3900

 

weighed at a different track, 3830

 

 

fyi, i dont do any race prep, so its not unsual for me to race with my tools in the trunk

[streetdreams]

"fyi, i dont do any race prep, so its not unsual for me to race with my tools in the trunk"

fk yeah!!! nothin like tellin a guy 'y'know it was close win but I want you to know it coulda been worse, I did have 100lbs of hammers and nails in the trunk" lmao

[john99gtp]

well, more like 70 lbs in the tool box, all my work stuff, usually 3/4 tank of gas, my old exhaust manifolds, spare tire and jack...the usual

[joey b]

no, the equation can deviate quite a bit from the actual. It would not be impossible to get a better time with less HP. Look at the L36 vs the LQ1, they have the same E/T but a difference of about 10% in HP. TQ is not at all figured into that equation. A sharp point in a power curve could show a high HP on a dyno, but if it is not very wide, you wouldn't have that good of a time.